1. Field of the Invention
The present invention relates to a display device having a flexible substrate.
2. Description of the Related Art
In recent years, active studies have been made of display devices such as liquid crystal devices and organic EL display devices. A glass plate is generally used in the display device to carry a display medium layer and the like. However, an attempt to use a flexible plastic plate has been made for the purposes of giving flexibility to the display device itself and reducing the thickness of the plate without deteriorating the plate strength.
Referring to a perspective view shown in FIG. 38, a common liquid crystal display device having a flexible plate will be explained. A liquid crystal display device 100 includes a first substrate 101, a second substrate 102 arranged to face the first substrate 101 and a liquid crystal layer as a display medium layer sealed between the first and second substrates 101 and 102 with a sealing member 103.
The first substrate 101 includes a plastic plate 111. A plurality of thin film transistors (TFTs, not shown) are formed on the surface of the plastic plate 111 facing the liquid crystal layer. Part of the first substrate 101 inside the sealing member 103 in which the liquid crystal layer is provided functions as a display area 120 which contributes to display. Further, part of the first substrate 101 outside the display area 120 serves as a mounting region 106 on which a driver IC chip 104 and a flexible printed circuit (FPC) 105 are mounted.
The second substrate 102 includes a plastic plate 112 and a polarizer 113 stacked on the surface of the plastic plate 112 facing outside (opposite the liquid crystal layer). In general, the second substrate 102 is shaped substantially the same as the display area 120. The mounting region 106 of the first substrate 101 protrudes outward beyond the edge of the second substrate 102 when viewed in plan.
As the plastic plates 111 and 112 are flexible, they are relatively greatly deformed even when a slight external force is applied thereto in the manufacture or use of the display device. There is a known technique of preventing the FPC from falling off due to the plate deformation by bonding a reinforcing plate separate from the other components with an adhesive such that the reinforcing plate overlaps part of the FPC bonded to the plastic plate (see, for example, Japanese Unexamined Patent Publication No. 61-65287). In the structure according to Japanese Unexamined Patent Publication No. 61-65287, a bottom surface of the bonded part of the FPC is bonded to the plastic plate with an anisotropic conductive connector interposed therebetween and a top surface of the bonded part of the FPC is bonded to the separate reinforcing plate with an adhesive. In this way, the adhesion of the FPC to the plastic plate is increased.
The mounting region 106 is made of a single plastic plate 111. Therefore, the mounting region 106 is less strong than the display area 120 made of the two plastic plates 111 and 112 bonded together and is prone to be relatively greatly deformed. As a result, when an external force is applied to the mounting region 106, bending stress is likely to concentrate on part of the plastic plate on which the sealing member 103 is provided as shown in the sectional view of FIG. 39.
The sealing member is generally harder than the flexible plastic plate and is less likely to be deformed. Therefore, the sealing member cannot be deformed along with the deformation of the flexible plate. That is, in the conventional display device, there is a possibility that the sealing member may fall off the flexible plate and a malfunction such as display failure may occur.
The reinforcing plate according to Japanese Unexamined Patent Publication No. 61-65287 is provided as a component separate from the other components (e.g., the second substrate). Therefore, the reinforcing plate is not effective at all against the bending stress concentrated on the part of the plate on which the sealing member is provided. To be more specific, it is difficult to prevent the sealing member from falling off with use of the reinforcing plate.